Push-button switch, keytop, and method of manufacturing the keytop

ABSTRACT

The keytop of a push-button switch includes a keytop portion situated on the top of a resin film, and a retaining portion situated on the underside of the resin film. The keytop portion and retaining portion are formed into a unitary body by a resin-molding process in which resin is passed through a hole provided in the resin film such that the resin film is sandwiched between the keytop portion and the retaining portion. In another embodiment, the retaining portion is loop-shaped and is formed into a unitary body with the keytop portion by a resin-molding process in which the resin passes through a plurality of holes provided in the resin film in a pattern corresponding to the loop-shaped circumference of the retaining portion. The resin film is sandwiched in a water-tight state between the keytop portion and the loop-shaped retaining portion.

This is a divisional application of U.S. ser. No. 07/046,172, filed Apr.14, 1993 which in turn is a divisional application of U.S. Ser. No.07/784,000 filed Oct. 29, 1991, U.S. Pat. No. 5,280,146.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the keytop of a push-button switch, a methodof manufacturing the keytop, and the push-button switch which uses thekeytop.

2. Description of the Prior Art

The reduction in the size of electronic devices that has been achievedin recent years has been accompanied by a demand to reduce the size andthickness also of the push-button switches used on the control panels ofthese devices. In addition, electronic devices often are used in avariety of environments, and there is a need for a push-button switchhaving a so-called drip-proof structure, namely a structure whichprevents humidity and moisture from penetrating into the contact portionof the switch from the outside.

The conventional keytop of the push-button switch of this type has acomplicated structure, has a large number of component parts andpossesses a hinge mechanism of a prescribed length. Consequently, such akeytop does not lend itself to a reduction in size and thickness. Inaddition, a keytop of this kind is not well suited for use in a switchhaving the aforementioned drip-proof structure which prevents externalhumidity and moisture from invading the contact portion through thekeytop.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the foregoing pointsand its object is to provide a keytop to which the small size andthickness of a push-button switch can be attributed as well as a methodof manufacturing such a keytop.

Another object of the present invention is to provide an outstandingpush-button switch having a drip-proof structure in which thepenetration of humidity and moisture from the keytop can be prevented,the number of component parts is few and which lends itself to areduction in size and thickness, as well as keytop of this push-buttonswitch and a method of manufacturing the keytop.

According to the present invention, there is provided a keytop of apush-button switch, in which a keytop portion is situated on the top ofa resin film at a prescribed position thereof, a retaining portion issituated on the underside of the resin film at a prescribed positionthereof, the keytop portion and the retaining portion are integratedthrough a portion of the keytop passing through a hole provided in theresin film and are formed by resin-molding, and the resin film issandwiched between the keytop portion and the retaining portion.

The retaining portion has the shape of a loop, the keytop portion andloop-shaped retaining portion are formed integrally by resin-molding,and the resin film is water-tightly sandwiched between the keytopportion and the loop-shaped retaining portion.

In another aspect of the invention, there is provided a keytop of apush-button switch in which a loop-shaped, drip-proof frame isresin-molded to be formed in a liquid-tight state with a resin film soas to surround a predetermined area of the resin film, a keytop portionis situated on top of the resin film within the loop-shaped, drip-proofframe at a prescribed position, a retaining portion is situated on anunderside of the resin film within the loop-shaped, drip-proof frame ata prescribed position, the keytop portion and the retaining portion areformed integrally by resin-molding, and the resin film is water-tightlysandwiched between the keytop portion and the retaining portion.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) through 1(C) are diagrams illustrating a first embodiment ofthe structure of a keytop of a push-button switch according to thepresent invention, in which FIG. 1(A) is a plan view, FIG. 1(B) asectional view taken along line 1(B)--1(B) of FIG. 1(A), and FIG. 1(C) abottom view;

FIG. 2 is a partial sectional view of a push-button switch which usesthe keytop of the present invention;

FIG. 3 is a plan view of a control panel of push-button switches havingthe keytop structure and drip-proof frame structure of the presentinvention;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3;

FIG. 5 is a bottom view of the control panel of the push-buttonswitches, in which the keytop structure and the structure of thedrip-proof frame are illustrated;

FIG. 6 is a sectional view taken along line 6--6 of FIG. 3;

FIG. 7 is a plan view of a resin film showing the shapes of holestherein;

FIG. 8 is a diagram showing the shapes of holes in a resin film whichforms a keytop;

FIG. 9 is a diagram for describing a method of manufacturing the keytop;

FIG. 10 is a diagram for describing a method of manufacturing thedrip-proof frame;

FIGS. 11(A) through 11(D) are diagrams illustrating a second embodimentof the structure of a keytop of a push-button switch according to thepresent invention, in which FIG. 11(A) is a plan view, FIG. 11(B) asectional view taken along line 11(B)--11(B) of FIG. 11(A), FIG. 11(C) abottom view, and FIG. 11(D) is a plan view of a resin film provided withholes;

FIGS. 12(A) through 12(C) are diagrams illustrating a third embodimentof the structure of a keytop of a push-button switch according to thepresent invention, in which FIG. 12(A) is a plan view, FIG. 12(B) asectional view taken along line 12(B)--12(B) of FIG. 12(A), and FIG.11(C) a bottom view;

FIG. 13 is a partial sectional view another embodiment of a push-buttonswitch according to the present invention;

FIG. 14 is a plan view of a resin film of the switch showing the shapesof holes in the resin film;

FIG. 15 is a diagram showing the shapes of holes in a resin film whichforms a keytop;

FIGS. 16(A) and 16(B) are diagrams for describing a method ofmanufacturing the keytop;

FIGS. 17(A) through 17(C) are diagrams illustrating another structure ofa keytop of a push-button switch according to the present invention, inwhich FIG. 17(A) is a plan view, FIG. 17(B) a sectional view taken alongline 17(B)--17(B) of FIG. 17(A), and FIG. 17(C) a bottom view;

FIG. 18 is a diagram showing still yet another embodiment of apush-button switch having a drip-proof structure according to thepresent invention;

FIG. 19 is a plan view of a switch control panel;

FIG. 20 is a sectional view taken along line 20--20 of FIG. 19;

FIG. 21 is a bottom view of the switch control panel;

FIG. 22 is a sectional view taken along line 22--22 of FIG. 19;

FIGS. 23(A) through 23(C) are plan, sectional and bottom views,respectively, of a keytop according to the present invention;

FIG. 24 is a plan view of a resin film showing the shapes of holes inthe resin film;

FIG. 25 is a plan view of a sheet from which upper and lower resinsheets constituting a switch portion are formed;

FIG. 26 is a diagram illustrating the resin mold of a keytop;

FIG. 27 is an exploded, perspective view of still another embodiment ofa push-button switch using the keytop of the invention;

FIG. 28 is an enlarged perspective view of a portion of a switch sheetshown in FIG. 27;

FIG. 29 is a perspective view of a keytop sheet;

FIG. 30 is a perspective view of a film;

FIGS. 31(A) through 31(C) are diagrams illustrating a method of moldinga keytop on a film, in which FIG. 31(A) is a diagram showing the mannerin which a film is clamped by upper and lower molds, FIG. 31(B) is adiagram illustrating the manner in which the upper and lower molds arefilled with a synthetic resin, and FIG. 31(C) is a diagram showing amolded keytop;

FIG. 32 is a sectional view of an assembled push-button switch:

FIG. 33 is an enlarged side sectional view showing a portion of onepush-button switch within a push-button switch;

FIG. 34 is a similar sectional view for describing the operation of thepush-button switch;

FIG. 35 is a perspective view showing a seventh embodiment of thestructure of a keytop sheet according to the present invention;

FIGS. 36(A), 36(B), 36(C) and 36(D) are a plan view of the keytop sheetof FIG. 35, a bottom view of the keytop sheet, an enlarged sectionalview taken along line 36(C)--36(C) of FIG. 36(A), and an enlargedsectional view taken along line 36(D)--36(D) of FIG. 36(A),respectively; and

FIGS. 37(A) through 37(C) are diagram for describing a method ofmanufacturing the keytop sheet, in which FIG. 37(A) is a diagram showinga flexible film, FIG. 37(B) is a diagram showing the manner in whichpatterns are printed on the film, and FIG. 37(C) is a diagram showingthe manner in which patterns are formed on the film as well as themanner in which openings and through-holes are provided in the film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1(A) through 1(C) are diagrams illustrating a first embodiment ofthe structure of a keytop of a push-button switch according to thepresent invention.

As shown in FIGS. 1(A) through 1(C), a keytop 12 includes a keytopportion 12b situated on the top side of a resin film 10, and aloop-shaped retaining portion 12c situated on the underside of the resinfilm. The loop-shaped portion 12c, which is located directly below thekeytop portion 12b in concentric relation therewith, is circular andextends along the outer circumference of the bottom surface of thekeytop portion 12b.

As will be described later in greater detail, the keytop portion 12b andloop-shaped retaining portion 12c are integrally formed by aresin-molding molding process in which resin is pass through a pluralityof holes provided in the resin film 10 in a pattern corresponding to theshape of the loop-shaped retaining member 12c. In this way, and theresin film 10 is water-tightly sandwiched between the keytop portion 12band the loop-shaped portion 12c.

A polycarbonate resin or acrylic resin, which are thermoplastic resins,may be used as the material for the keytop 12.

The keytop 12 has a pressing protrusion 12a, which is for pressing amovable contact, provided as an integral part of the loop-shapedretaining member 12c spaced away from the center of the button surfaceof the keytop portion 12b.

Thus, the pressing protrusion 12a for pressing the movable contact isprovided at a position offset from the center of the bottom surface ofkeytop portion 12b. As a result, it is unnecessary to dispose thecontact portion of the switch below the center of the bottom surface ofpressing protrusion 12a.

Accordingly, by using a keytop material through which light can pass, aswill be described later, the surface of the keytop can be made to standout by light from a light-emitting element if such an element is placedbelow the central portion of the bottom of the keytop portion 12b. Morespecifically, by printing a number, symbol or other indicia on theportion of the resin film 10 at which the keytop portion 12b is located,the number, symbol or indicia will be clearly visible through the keytopportion 12b. Such a keytop presents an excellent appearance.

Though the material of the keytop 12 is a light-transmissive resin whichis illuminated by a light-emitting element in the foregoing embodiment,the indicia on the keytop can readily be seen from the outside evenwithout being illuminated by a light-emitting element.

FIG. 2 is a diagram illustrating an example of the structure of apush-button switch using the keytop 12 having the structure describedabove.

In FIG. 2, numerals 16, 17 denote films on which a movable contactpattern 16a and a fixed contact pattern 17a, respectively, are formed.The films 16, 17 are superimposed with the contact patterns 16a, 17amade to oppose each other through the intermediary of a spacerinterposed therebetween, and the films 16, 17 are secured to the lowerportion of a drip-proof frame 11. A click spring 19 is disposed on thetop side of the film 16 at the position where the contact pattern 16a islocated, and the pressing protrusion 12a of the keytop 12 is situated onthe upper portion of the click spring 19. A light-emitting element 28,such as a light-emitting diode, is disposed below the center of thekeytop portion 12b.

The aforementioned drip-proof frame 11 surrounds a plurality of thekeytops 12 and is maintained in a water-tight state with respect to theresin film 10, as will be described later. The assembly which includesthe keytops 12, drip-proof frame 11 and films 16, 17 defines a controlpanel 1, which is housed in a case 15.

A panel 14 is placed upon the upper portion of the case 15 and isprovided with an elongate projection 14a that is water-tightly fittedinto an elongate groove 11a formed in the drip-proof frame 11.

The material constituting the drip-proof frame 11 is a thermoplastic orthermosetting synthetic resin. In order to improve the water-tight fitof the frame 11, the material constituting the frame preferably is aresilient styrene-type elastomer or a resilient polyester elastomer.

By adopting the foregoing structure for the push-button switch, humidityor moisture which seeps in from the gap between the keytop 12 and thepanel 14 will not reach the switch contact portion because the keytop 12and drip-proof frame 11 are water-tightly affixed to the resin film 10.

In addition, since the elongate groove 11a and elongate projection 14aare fitted together water tightly, moisture will not penetrate frombetween the drip-proof frame 11 and panel 14. The push-button switchthus has a structure exhibiting an excellent drip-proof property.

FIGS. 3 through 6 are diagrams illustrating the structure of the controlpanel 1 of the push-button switches obtained by molding the drip-proofframe 11 and keytops 12 with the resin film. FIG. 3 is a plan view, FIG.4 a sectional view taken along line 4--4 of FIG. 3, FIG. 5 an undersideview of the control panel 1, and FIG. 6 a sectional view taken alonglines 6--6 of FIG. 3.

As shown in these drawings, the drip-proof frame 11 surrounds aplurality (six in this embodiment) of the keytops 12 and is maintainedin a water-tight state with respect to the resin film 10.

More specifically, as shown in FIG. 6, the drip-proof frame 11 includesan upper portion 11b and a lower portion 11c formed to sandwich theresin film 10 therebetween, and the elongate groove 11a, which has arectangular cross section, is formed in the top of the upper portion11b. Further, as depicted in FIG. 5, the underside of the drip-proofframe 11 is integrally formed to have fixing portions 13 for being fixedto a substrate or the like.

Here the drip-proof frame 11 is such that the resin film 10 issandwiched between the loop-shaped upper portion 11b and loop-shapedlower portion 11c, and the upper portion 11b and lower portion 11c aremerely connected through holes 20 shown in FIGS. 6 and 7. Consequently,humidity and moisture cannot seep in from between the drip-proof frame11 and the resin film 10. In other words, a water-tight structure whichkeeps out humidity and moisture is formed between the resin film 10 andthe drip-proof frame 11.

Described next will be a method of manufacturing the switch controlpanel 1 by integrally molding the drip-proof frame 11 and keytop 12 withthe resin film 10. FIG. 7 is a plan view showing the external form ofthe resin film 10.

As shown in FIG. 7, the resin film 10 is rectangular and the portionthereof on which the drip-proof frame 11 is formed is provided atprescribed intervals with a number of holes 20 through which moltenresin flows at the time of molding.

As illustrated in FIGS 7 and 8, holes 21 for forming the keytop 12include small holes 21a and one large hole 21b in a circular array. Thesmall holes 21a are situated at ribs 12d of the keytop 12, and the largehole 21b is situated at the protrusion 12a of the keytop 12.

If required, a number, symbol or character 24 is printed on the resinfilm 10 at a portion thereof where the keytop portion 12b is located.The printing can be performed on either tile top side of the resin film10, namely on the side facing the keytop, or on the underside of theresin film 10. In either case, the number, symbol or character will beclearly visible.

A method of manufacturing the keytop 12 will now be described.

First, as shown in FIG. 9, the resin film 10 is clamped between an uppermold 105 having a cavity 110 of the same shape as the keytop 12 (seeFIG. 1) and a lower mold 106 having a cavity 111 of the same shape asthe annular retaining portion 12c (see FIG. 1).

Next, a molten resin is injected from a pin gate 107 provided at alocation above the protrusion 12a of the keytop 12. As a result, themolten resin flows into the cavity 110 of time upper mold 105 and alsointo the cavity 111 of the lower mold 106 through the holes 21a, 21b inthe resin film 10.

When the upper mold 105 and lower mold 106 are parted after the resinhas hardened, the result is the keytop 12.

A method of manufacturing the drip-proof frame 11 will be describednext.

First, as depicted in FIG. 10, the resin film 10 is clamped between anupper mold 101 having a cavity 112 of the same shape as the upperportion 11b of the frame (see FIG. 6) and a lower mold 102 having acavity 113 of the same shape as the lower portion 11c of the frame (seeFIG. 6).

Next, a molten resin is injected from a pin gate 103, whereby the moltenresin flows into the cavity 112 of the upper mold 101 through a resinreservoir 22 and also into the cavity 113 of the lower mold 102 throughthe holes 20 in the resin film 10.

When the upper mold 101 and lower mold 102 are parted after the resinhas hardened, the result is the drip-proof frame 11, which surrounds aprescribed area of the resin film 10.

FIGS. 11(A) through 11(D) are diagrams illustrating a second embodimentof the structure of a keytop of a push-button switch according to thepresent invention, in which FIG. 11(A) is a plan view, FIG. 11(B) asectional view taken along line 11(B)--11(B) of FIG. 11(A), FIG. 11(C) abottom view, and FIG. 11(D) is a plan view of a resin film provided withholes.

A keytop 12-2 shown in FIG. 11(A) differs from the keytop 12 of FIG. 1in that whereas the pressing protrusion 12a for pressing the movablecontact of the keytop 12 is provided as an integral part of theloop-shaped retaining portion 12c offset from the center of the lowerportion of the keytop portion 12b in FIG. 1(A), the keytop of FIGS.11(A)-11(D) is such that a pressing protrusion 12-2a passes through theresin film 10-2 approximately at the center of the lower portion of thekeytop portion 12-2.

Furthermore, since the pressing protrusion 12-2a is formed approximatelyat the center of the lower portion of the keytop portion 12-2, the resinfilm 10-2 at the location situated at the center of the keytop 12-2 iscut away in the form of a circle.

It should be noted that the shapes of the keytop portions 12b, 12-2b ofthe keytops 12 and 12-2 are not limited to those described in theforegoing embodiments. For example, it goes without saying that theplanar configuration can be rectangular or polygonal and need not becircular. In this case, the retaining portions 12c, 12-2c also shouldhave a rectangular or polygonal loop shape to conform to the shape ofthe keytop portion.

In addition, the shape of the drip-proof frame 11 is not limited to thatdescribed above. For example, if the drip-proof frame is made of anelastomer having resilience, then a structure may be adopted in whichthe panel 14 is flat, the surface of the drip-proof frame 11 is curvedin the shape of semicircular cylinder, and the panel 14 and frame 11 arebrought into pressing contact.

In other words, it will suffice if the loop-shaped drip-proof frame 11forms a water-tight seal together with the resin film by being moldedonto the resin film so as to surround a prescribed area of the film.

FIGS. 12(A) through 12(C) are diagrams illustrating a third embodimentof the structure of a keytop for a push-button switch according to thepresent invention. FIG. 12(A) is a plan view, FIG. 12(B) a sectionalview taken along line 12(B)--12(B) of FIG. 12(A), and FIG. 12(C) abottom view.

A keytop 12-3 has a keytop portion 12-3b consisting of a resin materialand formed as an integral part thereof, and integral film retainingportions 12-3c provided on the periphery of the keytop portion 12-3b.

A resin film 10-3 is disposed on the top of the keytop portion 12-3b soas to cover the same, and the resin film 10-3 is fixedly sandwichedbetween the film retaining portion 12-3c and film fixing portions 12-3dintegrally provided on the upper parts of the film retaining portions12-3c.

A thermoplastic polycarbonate resin or acrylic resin may be used as thematerial for the keytop 12-3.

The keytop 12-3 has a pressing protrusion 12-3a, which is for pressing amovable contact, integrally provided on the lower part of the filmretaining member 12-3c spaced away from the center of the button surfaceof the keytop portion 12-3b.

Thus, the pressing protrusion 12-3a for pressing the movable contact isprovided at a position offset from the center of the bottom surface ofkeytop portion 12-3b. As a result, it is unnecessary to dispose thecontact portion of the switch below the center of the bottom surface ofthe keytop portion 12-3b.

Accordingly, by using a light-transmissive resin material for the resinfilm and keytop, the surface of the keytop can be made to stand out bylight from a light-emitting element if such an element is placed belowthe keytop.

More specifically, by printing a number, symbol or other indicia asnecessary on the portion of the resin film 10-3 at which the keytopportion 12-3b is located, the number, symbol or indicia will be clearlyvisible above the keytop portion 12-3b. Such a keytop presents anexcellent appearance.

FIG. 13 is a diagram illustrating the structure of a push-button switchusing the keytop 12-3 having the structure shown in FIG. 12. Thispush-button switch is substantially the same as that of FIG. 2 and neednot be described again.

Described next will be a method of manufacturing a switch control panelobtained by integrally molding a drip-proof frame 11-3 and keytops withthe resin film 10-3.

FIG. 14 is a plan view showing the external form of the resin film 10-3.

As shown in FIG. 14, tile resin film 10-3 is rectangular and the portionthereof on which the drip-proof frame 11-3 is formed is provided atprescribed intervals with a number of holes 20-3 through which moltenresin flows at the time of molding.

Further, the portion of the resin film 10-3 on which the keytops 12-3are formed is provided at prescribed intervals with hole groups 21-3each having small holes 21-3a (at three locations in this embodiment)and one large hole 21-3b (at one location in this embodiment) throughwhich the molten resin flows.

If required, as shown in FIG. 15, a number, symbol or character 24-3 isprinted on the resin film 10-3 at a portion thereof where the keytopportion 12-3b is located. The printing can be performed either on thetop side or underside of the resin film 10-3.

FIG. 16(A) and FIG. 16(B) are diagrams showing a structure, in which theresin film is clamped between upper and lower molds, useful fordescribing the method of manufacturing a keytop according to thisembodiment. FIG. 16(A) is a cross sectional view of the molds 105-3,106-3 corresponding to a cross section of the keytop 12-3 taken alongline 12(D)--12(D) but not shown in FIG. 12(A), and FIG. 16(B) is across-sectional view corresponding to a cross section of the keytop 12-3taken along line 12(B)--12(B) of FIG. 12(A). As illustrated in thesedrawings, the resin film is clamped between an upper mold 105-3 and alower mold 106-3.

The upper mold 105-3 has a cavity 110-3 of tile same shape as tile upperpart of keytop portion 12-3b (see FIG. 12) and a cavity 112-3 of thesame shape as the film fixing portion 12-3d. The lower mold 106-3 has acavity 111-3 of the same shape as the lower part of keytop portion12-3b, a cavity 113-3 of the same shape as the film retaining portion12-3c, and a cavity 114-3 of the same shape as the pressing protrusion12-3a.

Thus, the resin film 10-3 is clamped by the upper mold 105-3 and thelower mold 106-3, and a molten resin is injected from a pin gate 107-3situated above the large hole 21-3b. As a result, tile molten resinflows into the cavities 114-3, 111-3 and 113-3 of the lower mold 106-3through the hole 21-3b formed in the resin film 10-3.

At this time, as shown in FIG. 16(B), those portions of the film 10-3which do not face the cavities 111-3, 113-3 and 114-3 formed in thelower mold 106-3 are strongly clamped by the upper and lower molds, andtherefore the molten resin which has flowed in deforms the film 10-3 andforces it into intimate adhering contact with the inner wall of theupper mold 105-3. The molten resin flows into the cavity 110-3 of theupper mold 105-3 and flows also into the cavity 112-3 of the upper mold105-3 through the hole 21-3a formed in the resin film 10-3.

As a result of the foregoing, the resin film 10-3 is deformed and comesinto intimate adhering contact with the inner wall of the cavity 110-3of upper mold 105-3, as indicated by the dashed line.

When the upper mold 105-3 and lower mold 106-3 are parted after themolten resin has hardened, the result is the keytop 12-3, in which thesurface of the keytop portion 12-3b is covered with the resin film, asillustrated in FIGS. 12(A) through 12(C).

In the embodiment described above, the upper mold 105-3 is provided withthe pin gate 107-3, and the molten resin is charged into the cavities111-3,113-3 and 114-3 of the lower mold 106-3 through the large hole21-3b formed in the resin film 10-3. However, it is permissible toprovide a pin gate opening to the cavity 114-3 of the lower mold 106-3and to charge the molten resin directly into the cavity 114-3.

The gist of the method of manufacture according to this embodiment ofthe invention resides in molding the keytop 12-3 in the resin film 10-3while the resin film is deformed into the shape of the cavity 110-3.Accordingly, the results are influenced by the shape of the keytop 12-3and the charging conditions of the molten resin.

According to this embodiment, a keytop was manufactured in which thethickness of the resin film was 0.2 mm and the height of the keytop 12-3was made less than 1/2 the diameter. The result was that the resin film10-3 was deformed into intimate contact with tile inner wall of thecavity 110-3 of upper mold 105-3, as indicated by the dashed line.

For charging of the molten resin, it is necessary to set the temperatureof the molten resin, the injection (charging) pressure, the injectionspeed, the injection time and the temperature of the molds to suitablevalues. In this embodiment, molding at a high yield was achieved bysetting the temperature of the molten resin to 240° C., the moldtemperature to about 80° C., the injection time to about 3 sec, coolingtime to about 10 sec, the injection pressure of the injection moldingmachine to 1400 kg, and the injection speed to 15 mm/sec.

FIGS. 17(A) through 17(C) are diagrams illustrating a fourth embodimentof the structure of a keytop for a push-button switch according to thepresent invention. FIG. 17(A) is a plan view, FIG. 17(B) a sectionalview taken along line 17(B)--17(B) of FIG. 17(A), and FIG. 17(C) abottom view.

A keytop 12-4 has a keytop portion 12-4b consisting of a resin materialand an integral film retaining portion 12-4c provided on the peripheryof the keytop portion 12-4b.

As in the keytop shown in FIGS. 12(A)-(C), the resin film 10-4 in thisembodiment is disposed on the top of the keytop portion 12-4b so as tocover the same, and the resin film 10-4 is fixedly sandwiched betweenthe film retaining portion 12-4c and a film fixing portion 12-4dintegrally provided on the upper part of the film retaining portion12-4c.

This keytop 12-4 differs from the keytop of FIGS. 12(A)-(C) in that apressing protrusion 12-4f which presses the movable contact is projectsbeyond the underside of the film retaining portion 12-4c at the centerof the lower part of tile keytop portion 12-4b.

Also, as in the keytop 12 of FIG. 1, a thermoplastic polycarbonate resinor acrylic resin may be used as the material for the keytop 12-4.Furthermore, the only difference in the method of manufacture is thatthe shape of the cavity in the lower mold corresponds to the shape ofthe keytop 12-4. In other aspects, the method of manufacture is the sameas that for the keytop of FIG. 1 and need not be described again.

In this embodiment, a light-transmissive resin material is used for theresin film 10-4 and keytop 12-4. By printing a number, symbol or otherindicia as necessary on the portion of the resin film 10-4 at which thekeytop portion 12-4b is located, the number, symbol or indicia will beclearly visible. Such a keytop presents an excellent appearance.

It should be noted that the shape of the keytop portion 12-4b of thekeytop 12-4 is not limited to that described in the foregoingembodiment. For example, it goes without saying that the planarconfiguration can be rectangular or polygonal and need not be circular.

Further, although four of the film retaining portions 12-4c are providedin a radiating fashion on the outer circumference of the keytop portion12-4b on the bottom thereof, the film retaining portions 12-4c are notlimited to this arrangement. In order to increase the strength ofadherence between the keytop 12-4 and the resin film 10-4, the number ofradiating film retaining portions 12-4c may be increased. In addition,the film fixing portions 12-4d may be connected in the form of a ring.

In other words, so long as the resin film 10-4 is capable of beingstrongly clamped by the upper mold 105-4 and lower mold 106-4 at thelocations of the keytop 12-4, the film retaining portions 12-4c and filmfixing portions 12-4d may be of any number and of any shape.

FIG. 18 is a sectional view showing a fifth embodiment of a push-buttonswitch according to the present invention. In FIG. 18, numeral 29denotes a substrate, located at the corner portion of an electronicappliance for example. Upper and lower resin sheets 16-5, 17-5 having aspacer 18-5 interposed therebetween them are arranged on top of thesubstrate 29. The lower resin sheet 17-5 has a fixed-contact pattern17-5a of a switch, and the upper resin sheet 16-5 is formed to have amovable contact 16-5a of the switch. The fixed contact 17-5a and themovable contact 16-5a oppose each other.

A click spring 19-5 is disposed at a location where the movable contactof the upper resin film 16-5 is formed, and a keytop 12-5 providedwater-tightly on the resin film 10-5 is disposed on the click spring19-5, as will be described later in greater detail.

Numeral 11-5 denotes a drip-proof frame provided water-tightly on theresin film 10-5 so as to surround a prescribed area of the film, as willbe described later.

Numeral 14-5 designates a panel, which defines a curved surface. Theupper portion of the keytop 14-5 penetrates a hole 24A provided in thepanel 12-5 and is exposed from above. As will be set forth later, thedrip-proof frame 11-5 and tile panel 14-5 are fitted together in awater-tight state by mating a projection with a groove. The drip-proofframe 11-5 also is attached to the substrate 29 in a water-tight state.

The arrangement is such that pressing the keytop 12-5 causes the movablecontact 16-5 to come into abutting contact with the fixed contact 17-5a.

As will be set forth below, the keytop is attached to the resin film10-5 in a water-tight state, and the drip-proof frame 11-5 is attachedto the resin film 10-5 in a water-tight state. As a result, thestructure is such that moisture or humidity which seeps in from holes inthe panel 14-5 will not invade the contact portion, which comprises theresin sheet 16-5, 17-5 and the like. The structure of each portion ofthe push-button switch constructed as set forth above will now bedescribed in detail.

As illustrated in FIGS. 19 through 22, the loop-shaped drip-proof frame11-5 is formed on the resin film 10-5 by being molded with the film 10-5in a water-tight state so as to surround a prescribed area of the film.The keytop 12-5 is formed within the drip-proof frame 11-5 in awater-tight state with respect to the resin film 10-5.

As shown in FIG. 22, the drip-proof frame 11-5 has an upper portion11-5b and a lower portion 11-5c which sandwich the resin film 10-5between them. The top side of the upper portion 11-5b is formed to havean elongated groove 11-5a having a rectangular cross section, and afixing portion 11-5d for being fixed to the substrate is formed as anintegral part of the underside of tile drip-proof frame 11-5.

Here the drip-proof frame 11-5 is formed so that the resin film 10-5 issandwiched between the loop-shaped upper portion 11-5b and loop-shapedlower portion 11-5c, and the upper and lower portions 11-5b, 11-5c areintegrally connected through a hole 20-5 formed in the resin film 10-5.Consequently, humidity and moisture cannot seep in from between thedrip-proof frame 11-5 and the resin film 10-5. In other words, awater-tight structure which keeps out humidity and moisture is formedbetween the resin film 10-5 and the drip-proof frame 11-5.

The material constituting the drip-proof frame 11-5 is a resilientsynthetic resin, such as a styrene-type elastomer or a polyesterelastomer.

As depicted in FIGS. 23(A)-(C), the keytop 12-5 includes a keytopportion 12-5b forming the upper portion of the keytop and an annularretaining portion 12-5c forming the lower portion so as to sandwich theresin film 10-5, and the underside is formed to have a protrusion 12-5afor pressing the movable contact of the switch. The materialconstituting the keytop 12-5 consists of a thermoplastic resin, namelypolycarbonate resin or acrylic resin.

Here the keytop 12-5 is such that the resin film 10-5 is sandwichedbetween the keytop portion 12,5b and the annular retaining portion12-5c, and the keytop portion 12-5b and annular retaining portion 12-5care integrally connected through holes a hole 21-5 shown in FIG. 23(B).FIG. 24 is a plan view of a resin film 10-5 having the holes 20-5 forfacilitating the molding the drip-proof frame 11-5, the holes 21-5 forfacilitating the molding the keytops 12-5, and holes 22 through whichthe protrusions 12-5a project. Consequently, humidity and moisturecannot seep in from between the keytop 12-5 and the resin film 10-5. Inother words, a water-tight structure which keeps out humidity andmoisture is formed between the resin film 10-5 and the keytop 12-5.

FIG. 25 is a plan view showing the shapes of the upper and lower resinsheets 16-5, 17-5. As shown in FIG. 25, the upper and lower resin sheets16-5, 17-5 are formed of a single resin sheet cut to the shape shown inthe figure.

Formed on the lower resin sheet 17-5 are fixed-contact patterns 17-5a,17-5a, 17-5a and a wiring pattern 17-5b serially connecting thefixed-contact patterns 17-5a, 17-5a, 17-5a. Formed on the upper resinsheet 16-5 are movable-contact patterns 16-5a, 16-5a, 16-5a and wiringpatterns 16-5b, 16-5b, 16-5b connected to respective ones of themovable-contact patterns 16-5a, 16-5a, 16-5a. In order to facilitatefolding, the upper resin sheet 16-5 is provided with grooves 25-5between the movable-contact patterns 16-5a, 16-5a.

Cut-outs 23-5 are formed between the upper resin sheet 16-5 and thelower resin sheet 17-5. Contact portions are formed by folding the upperresin sheet 16-5 and lower resin sheet 17-5 about the cut-outs 23-5interposing the therebetween the spacer 18-5.

The formation of the keytop 12-5 by resin molding will be describedbelow.

As depicted in FIG. 26, the resin film 10-5 is clamped between an uppermold 105-5 having a cavity 110-5 of the same shape as the keytop portion12b. [see FIGS. 23(A) through 23(C)], and a lower mold 106-5 having acavity 111-5 of the same shape as the annular retaining portion 12-5c[see FIGS. 23(A) through 23(C)]and a cavity 112-5 of the same shape as aprotrusion 18-5a.

Next, a molten resin is injected from a pin gate 107-5, whereby themolten resin flows into the cavity 110-5 of the upper mold 105-5 and thecavity 112-5 of the lower mold 106-5. The molten resin flows also intothe cavity 111-5 of the lower mold 106-5 through holes 21-5 in the resinfilm 16-5.

The keytop 12-5 is formed by allowing the molten resin to harden. Theformation of the drip-proof frame 11-5 is substantially the same as themethod described in connection with FIG. 10 and need not be explainedagain.

The manner in which the push-button switch is mounted on the main bodyof an appliance will now be described. First, as shown in FIG. 18, theresin sheets 16-5, 17-5 on which the fixed-contact pattern 17-5a andmovable-contact pattern 16-5b are formed are folded about the cut-outs23-5 with the spacer 18-5 interposed between the folds, and the resinsheets thus folded are placed upon the curved surface of the substrate29.

Next, the fixing portions 11-5d (ten of which are provided in thisembodiment) of the drip-proof frame 11-5 are press-fitted into fittingholes provided in the surface of the substrate 29.

The reason for providing more than two pairs of the fixing portions11-5d in the longitudinal direction of the drip-proof frame 11-5 is sothat the switch control panel will be maintained at a fixed distancefrom the curved substrate surface. Next, a fitting projection 14-5aprovided on the curved panel 14-5 is fitted into the elongate groove11-5a formed in the top of the drip-proof frame 11-5. This completes themounting of the push-button switch in this embodiment.

FIG. 27 is an exploded, perspective view showing a sixth embodiment of apush-button switch using the keytop of the invention. As shown in FIG.27, a push-button switch 70 comprises, in a superimposed relation, alower case 60, a switch sheet 30, a keytop sheet 40 and an upper case50.

Each of the components constituting the push-button switch 70 will nowbe described.

A number of click plates 34 are attached to the top of the switch plate30, and a membrane switch is disposed on the underside of each switchplate.

FIG. 28 is an enlarged, exploded perspective view showing the portion A(one membrane switch) of the switch sheet 30 shown in FIG. 27.

The switch sheet 30 illustrated in FIG. 28 comprises a first substrate31 consisting of a resilient synthetic resin film provided with acontact pattern 31a at a predetermined position on the top thereof, anda spacer 32 consisting of a resilient synthetic resin film provided witha through-hole 32a at a predetermined position.

The switch sheet 30 further comprises a second substrate 33 providedwith a contact pattern 33a at a predetermined position of the undersidethereof. The substrates 31, 33 and spacer 32 are bonded together in sucha manner that the contact pattern 31a of the first substrate 31 and thecontact pattern 33a of the second substrate 33 will oppose each othervia the through-hole 32a of the spacer 32. The switch sheet 30 is thusconstructed.

It should be noted that one membrane switch is constructed at theportion where the fixed contact patterns 31a and 33a oppose each other.

The click plate 34, which consists of an upwardly bent resilient metalplate, is bonded to the top of the second substrate 33 at the positionwhere the two contact patterns oppose each other.

Further, as illustrated in FIG. 27, light-emitting elements 35 areattached to the top of the switch sheet 30 at prescribed positions.

Next, the keytop sheet 40 to which the present invention is applied isconstructed by directly attaching a number of keytops 41 to a film 45made of synthetic resin.

FIG. 29 is a perspective view showing the underside of the keytop sheet40.

As shown in FIGS. 27 and 29, each keytop 41 comprises an actuatingportion 41a formed on the top of the film 45, and a pressing portion 41bprotruding from the underside of the film 45. The actuating portion 41aand pressing portion 41b of the keytop 41 are integrally molded via ahole 46 provided in the film 45.

The method of manufacturing the keytop sheet 40 will be described next.

FIG. 30 is a perspective view showing the film 45. As shown in FIG. 30,the film 45 is of a synthetic resin formed as a flexible thin sheet andis provided with small holes 46 at positions corresponding to the clickplates 34 of the switch sheet 30 shown in FIG. 27.

FIG. 31(A) through FIG. 81(C) are diagrams illustrating a method ofresin molding the keytops 41 on the film 45. It should be noted thatFIG. 31 illustrates only one keytop 41 among the plurality thereof.

First, as depicted in FIG. 31(A), the film 45 is clamped from above andbelow by an upper mold 105 and a lower mold 106-6. The portion of theupper mold 105-6 corresponding to the hole 46 is provided with a cavity110-6 for molding the actuating portion 41a of the keytop 41. The uppermold 105-6 is provided also with a pin gate 107-6 in the vicinity of theouter circumference of the cavity 110-6. The portion of the lower mold106-6 corresponding to the hole 46 is provided with a cavity 111-6 formolding the pressing portion 41-b of the keytop 41.

Next, as shown in FIG. 31(B), a synthetic resin is injected from the pingate 107-6 so as to fill the cavities 110-6 and 111-6.

As illustrated in FIG. 81(C), the upper mold 105-6 and lower mold 108-6are removed after the injected synthetic resin has hardened. Thiscompletes the formation of the keytop 41 on which the actuating portion41a and pressing portion 41b are integrally molded via the hole 46 offilm 45.

When the keytop 41 is thus directly molded on the film 45, the undersideof the actuating portion 41a of the keytop is closely adhered to the topside of the film, and the top side of the pressing portion 41b is closedadhered to the underside of the film 4S.

Next, the upper case 50 shown in FIG. 27 is molded out of syntheticresin, and upper case 50 is provided with circular holes 51 at positionscorresponding to the keytops 41.

The lower case 60 shown in FIG. 27 is then formed from a metal plate theperiphery of which is provided with an upstanding edge 63. Portions ofthe upstanding edge 63 are provided with tabs 61, each of which has amounting hole 62.

In order to assemble the push-button switch 70, the switch sheet 30 isplaced upon the lower case 60, as shown in FIG. 27. An adhesive isapplied to an adhering surface 47 (the entire periphery of the top offilm 45) of the keytop sheet 40, and the keytop sheet 40 is bonded tothe underside of the upper case 50. The upper case 50 is then placedupon the lower case 60 and secured thereto to complete the constructionof the push-button switch 70.

FIG. 32 is a side sectional view illustrating the push-button switch 70thus assembled. As illustrated in FIG. 32, a screw 71 is inserted intothe mounting hole 62 of the tab 61 provided on the lower case 60, thelower case 60 is fitted into the upper case 50 within the outercircumferential wall thereof, and the two cases are secured to eachother. The click plates 34 are situated beneath respective ones of thekeytops 41, as shown.

FIG. 33 is an enlarged side sectional view showing one push-buttonswitch portion of the push-button switch 70. The lower case 60, itshould be noted, is omitted from the drawing.

As shown in FIG. 33, the push-button switch 70 is such that the clickplate 34 and corresponding keytop 41 are arranged above a membraneswitch composed of a contact pattern 31a and a contact pattern 33a whichoppose each other via the through-hole 32a of the spacer 32.

If the actuating portion 41a of the keytop 41 is pressed, as illustratedin FIG. 34, the film 45 is flexed and presses against the click plate34, which performs a snap action. In addition, the second substrate 33is pressed downward and causes the contact pattern 33a to contact thecontact pattern 31a, thereby turning on (i.e., closing) the twocontacts.

When tile pressing force is removed from the keytop 41, the latter isrestored to tile original position by a restoration force which attemptsto return the click plate 32 and film 45 to their original states. As aresult, the membrane switch is turned off (i.e. opened).

In this embodiment of the present invention, as described above, theunderside of the actuating portion 41a of keytop 41 and the top side ofthe pressing portion 41b are closely adhered to the upper and lowersurfaces of the film 45, and therefore gaps do not form between the film45 and the keytop 41. That is, the hole 46 provided in the film 45 isplugged by the keytop 41. Consequently, even if a water droplet invadesthe keytop 41 or film 45 from the hole 51 in the upper case 50, thewater droplet will not seep down into the switch from the hole 46 in thefilm 45.

Further, in the present invention, the fact that a number of the keytops41 are directly molded on the thin film 45 makes it possible toconsiderably reduce the thickness of the group of keytops 41.

If the keytop 41 consists of a light-transmissive material, lightemitted by the light-emitting element 35 shown in FIG. 27 will beintroduced to the interior of the keytop 41 to clearly illuminate thesame.

Although an example of a push-button switch using the keytop accordingto the present invention has been described in detail, the invention isnot limited to the illustrated arrangement, and various modificationsare possible, as set forth below.

Although the switch arranged below the keytop is a membrane switch inthe foregoing embodiment, the switch of the invention is not limitedthereto. A membrane switch of a different structure may be employed, andthe push-button switch may be provided with a structure other than thatof a membrane switch.

The shape of the keytop is not limited to that or the foregoingembodiment. As long as a film is provided with a plurality of holes andthe keytop extends from the top to the underside of the film via eachhole, the keytop may have any desired shape.

FIG. 35 is a perspective view showing a seventh embodiment of a keytopsheet according to the present invention.

As shown in FIG. 35, a keytop sheet 40-7 is constructed by directlymolding three keytops 41-7 on a film 45-7 made of synthetic resin. FIGS.36(A) through 36(C) are diagrams illustrating the keytop sheet 40-7, inwhich FIG. 36(A) is a plan view, FIG. 36(B) a bottom view, FIG. 36(C) anenlarged sectional view taken along line 36(C)--36(C) of FIG. 36(A), andFIG. 36(D) an enlarged sectional view taken along line 36(D)--36(D) ofFIG. 36(A).

The keytop sheet 40-7 shown in FIG. 36 includes a flexible, transparentfilm 45-7 made of synthetic resin (e.g., polyethylene terephthalate)provided with holes 45-7a at four locations. Each pair of adjacent holes45-7a forms a respective recess through the film 45-7. Keytops 41-7 madeof synthetic resin are directly molded on three circular keytop-mountingsurfaces of the film each disposed in a respective recess formed by twoof the holes 45-7a.

Each keytop 41-7 is molded from a transparent synthetic resin andincludes an actuating portion 41-7a provided on the top of the film45-7, three film fixing portions 41-7b provided on the underside of thefilm 45-7 via holes 45-7c provided in the film 45-7, and a protrudingportion 41-7c provided on the underside of the film 45-7.

As shown in FIG. 36(A), if required a prescribed light-transmissivesymbol 46-7b is printed on the underside of the film 45-7 to which thekeytop 41-7 is attached (namely the underside of the keytop-mountingsurface 45-7e of film 45-7), and the periphery of the symbol 46-7b isprinted so as to have an opaque portion 46-7a (indicated by the hatchingin FIG. 36(B)).

Accordingly, the symbol 48-7b is visible from the top side of the keytop41-7 via the transparent film 45-7 and actuating portion 41-7a. Ifilluminated with light from the lower side of the film 45-7, the symbol46-7b shows up very clearly.

The method of manufacturing the keytop sheet 40-7 will now be described.

FIG. 37(A) through FIG. 37(C) are diagrams showing the method ofmanufacturing the keytop sheet 40-7.

First, as shown in FIG. 37(A), a thin, flexible film 45-7 consisting ofa polyethylene sheet is prepared. Next, as illustrated in FIG. 37(B), aprescribed pattern 47-7 is printed at a predetermined position on thefilm 45-7 (namely on a portion of the film which will become thekeytop-mounting surface 45-7e in the following step). As illustrated,the pattern 47-7 is constituted by a circular opaque portion 47-7a thatis black, by way of example, and a light-transmissive symbol 47-7b thatis white, for example.

Next, as depicted in FIG. 37(C), the holes 45-7a are provided in thefilm 45-7 to both sides of the portions furnished with the patterns 47-7(namely at the portions serving as the keytop-mounting surfaces 45-7e towhich the keytops 41-7 are attached), and the through-holes 45-7c areprovided at three locations for each of the keytop-mounting surfaces45-7e. A hinge portion of the resin film is formed of portions 45-7b,45-7b of the film left at opposite sides of each key-top mountingsurface 45-7e. Each hinge portion connects a keytop-mounting surface45-7e to a peripheral portion of the film 45-7 defining the periphery ofa recess.

The method of forming the keytops 41-7 of the keytop sheet 40-7 issubstantially the same as in FIG. 31 and need not be described again.

The keytop of the push-button switch according to the present inventionis not limited to that of the foregoing embodiment and can be modifiedin various ways.

In the present embodiment, the film 45-7 is transparent. However, solong as the character, number or symbol on the film 45-7 can be directlydistinguished from above the keytop, this will suffice. Therefore, ifthe material constituting the keytop is transparent or semi-transparent,the film 45-7 may be opaque.

One of the two portions of the film forming the hinge portion of eachswitch can be eliminated by cutting the film along line C--C shown inFIG. 37(C).

By constructing the keytops in the manner set forth above, the printingof the symbols is performed on tile film. As a result, it is unnecessaryto print characters, numbers or symbols on the keytops, as is done inthe prior art, thereby making it easy to perform printing.

In the prior art, it is necessary to print characters, numbers orsymbols on the keytops and attach a transparent sheet to the keytops toprotect these marks. By contrast, in accordance with the presentinvention, the keytops can be manufactured merely by being moldeddirectly on a film. As a result, not only is manufacture facilitated,but mass production is expedited manufacturing cost are reduced and thekeytops can be made much thinner.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A keytop sheet for use in a push-button switch,said keytop sheet comprising a synthetic resin film having a recesstherethrough, a hinge portion, and a respective keytop mounting portioncontiguous to said hinge portion, said keytop mounting portion beinglocated in said recess, said hinge portion connecting said keytopmounting portion to a peripheral portion of said resin film defining theperiphery of said recess such that said keytop mounting portion can bedepressed relative to said peripheral portion by a flexing of the hingeportion of said resin film, and a molded one-piece keytop mounted to thekeytop mounting portion of said resin film.
 2. A keytop sheet as claimedin claim 1, wherein said keytop includes a keytop portion situated onone side of the keytop mounting portion of said resin film, and aretaining portion situated on the other side of the keytop mountingportion of said resin film, the keytop mounting portion of said resinfilm has at least one hole therethrough through which a portion of saidkeytop extends from said keytop portion to said retaining portion, thekeytop mounting portion of said resin film being sandwiched in awater-tight state between said keytop portion and said retainingportion.
 3. A keytop sheet as claimed in claim 1, wherein said keytop istransparent, and the keytop mounting portion of said resin film has atransparent portion and an opaque portion surrounding said transparentportion.
 4. A push-button switch comprising: a fixed contact and amovable contact opposing each other, a synthetic resin film extendingover said contacts, and a molded one-piece keytop supported by saidresin film above said movable contact, said synthetic resin film havinga recess therethrough, a hinge portion, and a respective keytop mountingportion contiguous to said hinge portion, said keytop mounting portionbeing located in said recess, said hinge portion connecting said keytopmounting portion to a peripheral portion of said resin film defining theperiphery of said recess such that said keytop mounting portion can bedepressed toward said movable contact relative to said peripheralportion by a flexing of the hinge portion of said resin film, saidkeytop being mounted to the keytop mounting portion of said resin film.5. A push-button switch as claimed in claim 4, wherein said keytopincludes a keytop portion situated on one side of the keytop mountingportion of said resin film, and a retaining portion situated on theother side of the keytop mounting portion of said resin film, the keytopmounting portion of said resin film has at least one hole therethroughthrough which a portion of said keytop extends from said keytop portionto said retaining portion, the keytop mounting portion of said resinfilm being sandwiched in a water-tight state between said keytop portionand said retaining portion.
 6. A push-button switch as claimed in claim4, wherein said keytop is transparent, and the keytop mounting portionof said resin film has a transparent portion and an opaque portionsurrounding said transparent portion.